Helianthus annuus

Scientific Name Helianthus annuus L.
Common Names English: Sunflower; German: Sonnenblume; French: Tournesol; Spanish: Girasol
Description Tall, coarsly-leafed plant with a distinctive large, yellow bloom, growing to a height of 60 - 390 cm (1.97 - 12.79 ft) and forming a taproot. H. annuus is native to North America.

Descriptions

Characteristic Features

Large heart-shaped leaves.

Young Plant

Cotyledons oblong, 15-40 mm (0.59 - 1.57 inch) long, joined at the bases, smooth. First few true leaves opposite, dull green, covered with short bristly hairs that are rough to touch. Margins weakly round-toothed. Subsequent leaves alternate.

Cotyledons

Oblong, 15-40 mm (0.59 - 1.57 inch) long, joined at the bases, smooth.

Stems

Large, stout central stem.

Leaves

7.5 - 30 cm (2.95 - 11.81 inch) long; the lowest ovate, usually heart-shaped, edged with irregular teeth; the upper, smaller and narrower.

Propagatio Organs

Flowers

Large heads 7.5 - 15 cm (2.95 - 5.9 inch) wide.
More than 10 flowers per plant.
Ovate bracts enclose heads edged with bristles and narrow abruptly to a slender tip.
Flower made up of 1,000 to 2,000 individual flowers joined at a common receptacle. The flowers around the circumference are ligulate ray flowers without stamens or pistils. The remaining flowers are perfect flowers (with stamens and pistils).

Flowering Period

February-October.

Fruit

Achenes 3-15 mm (0.118 - 0.59 inch) long. Pappus scales 2-3.5 mm (0.078 - 0.137 inch) long. Dry casing enclosing a white seed; flattish but plump; drop off easily.

Seeds

Seedlings can emerge from depths of at least 10 cm (3.93 inch).
Germination in spring.

Viability Of Seeds

3-5 years.

Propagation

By seeds.
500-900 seeds/head.

Occurrence

Habitat

Woodland meadows, cultivated and abandoned fields, pastures, areas along railroads and roads, and urban waste areas, dry open plains and foothills.

Soil

Fertile loamy soil, often thrives in soil with a high clay or gravel content.

Agricultural Importance

H. annuus reduces significantly crop yield because of its aggressive growth habit, canopy structure and competitiveness. The leafs are inedible for humans and livestock because of high nitrogen content.

Control

Integrated Crop Management

Cultivation to a depth of 20 cm (7.87 inch) reduces survival of sunflower.

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